1. Field of the Invention
The present invention relates to fault detection in rotating field machines, including permanent magnet motor and induction motor drive systems, and relates more particularly to detection of phase loss in a rotating field machine.
2. Description of Related Art
Permanent magnet (PM) and induction motors and motor drive systems are known for use in a variety of applications involving motion and velocity control. Some types of motor drives include a power inverter that selectively delivers power to various phases in a multiphase motor. One type of motor uses three phases that are each excited according to a particular methodology to interact with a permanent magnet to drive the motor according to a desired profile. Due to design and other practical considerations, connections to the motor from the power inverter are often made with cables or wiring connections that may vary in length, such that the power inverter is separated from the motor. Precautions are typically taken to protect the cables and wiring connections from the impact of EMI and other noise signals that are often found in motor drive systems.
Despite the additional precautions usually taken in protecting the cables and wiring connections between the power inverter and the motor, problems with respect to the cables or wiring connections can sometimes occur. For example, drive operation failure occurs when wiring connections between drive and motor are broken, loose or misconnected. For example, any of the above problems may lead to motor startup failure.
In cases where a large starting torque is not required, the motor may start and continue to run, but with significant torque ripple. The torque ripple substantially reduces drive efficiency, increases audible noise and eventually may damage the connecting shaft load. It would be desirable to detect when a faulty motor electrical connection exists, and provide a failure response in that case.